In typical analog circuits such as DC-DC converters, internal bandgap and regulator circuits are commonly used to generated reference voltages and internal VCC voltages. As the name suggests, the voltages generated by the bandgap reference generators are used as references, and hence the outputted reference voltages need to be highly stable. To be specific, the outputted reference voltages need to be free from temperature variations, voltage variations, and process variations. Voltage regulators may also be connected to exploit the advantageous features of the highly stable reference voltages, and to regulate or convert the reference voltages to higher or lower stable voltages, for example, VCC voltages.
FIG. 1 illustrates a circuit diagram of a conventional bandgap and regulator circuit, which includes a bandgap reference generator and a voltage regulator. PMOS transistors M0′ and M1′ form a current mirror. Bipolar transistors Q0′ and Q1′ are used to compensate for the temperature variation in the resulting reference voltage VA′ at node A′. The generated reference voltage VA′ can be expressed as:VA′=ΔVBE×(R1+R0)/R0+VBE0  [Eq. 1]Wherein ΔVBE is equal to (VBE1−VBE0), with voltage VBE1 being the base-to-emitter voltage of bipolar transistor Q1′, and voltage VBE0 being the base-to-emitter voltage of bipolar transistor Q0′. Appropriate values are selected for the devices in the circuit shown in FIG. 1. For example, if a ratio of the area of bipolar transistor Q0′ to the area of bipolar transistor Q1′ is 8:1, and resistance ratio R1′:R0′ is 4, reference voltage VA′ equal to about 1.25V may be generated. Further, reference voltage VA′ may have a zero temperature coefficient at room temperature. The voltage regulator includes operational amplifier OP, PMOS transistor M10′, and resistors R3′ and R4′. By selecting resistor R3′ to have a same resistance as resistor R4′, the resulting voltage VCC may be about 2.5V. Voltage VCC has a smaller variation than the external voltage VIN′.
The conventional internal bandgap and regulator circuit as shown in FIG. 1, however, suffers from drawbacks. Due to the use of operational amplifier OP, the power consumption is high, and a great die area is required by the internal bandgap and regulator circuit. What is needed, therefore, is a bandgap and regulator circuit for overcoming the above-described shortcomings in the prior art.